The present invention relates to a parting composition comprising a mixture of glycerol trioleate and a vegetable oil. The composition is useful in casting ingots of aluminum and its alloys.
In the casting of aluminum and its alloys, it is customary to employ a mold lubricant and parting agent. Satisfactory ingot surface can be obtained only with a lubricant which has the ability to carry high loads at high temperatures. Until the mid-1950s, lard oil was commonly used as a mold lubricant for aluminum ingot casting. Mold design and lubricant application were not sophisticated and lard oil was often applied to molds by brushing or swabbing prior to casting. The principal disadvantages of lard oil is its tendency to harden to a grease-like consistency at approximately 40.degree. F. This precluded its use in modern continuous casting methods where free flowing lubricant is required for cold weather operations. In addition, ingot cooling water interacts with lard oil to produce a grease-like material which can build up on continuous casting belts, interfere with ingot cooling and cause environmental difficulties. With the advent of advanced casting methods including continuous casting, castor oil has replaced lard oil as the most commonly used mold lubricant. Castor oil does not suffer the above-mentioned disadvantages of lard oil. However, pure castor oil is very viscous and difficult to apply to molds in a uniform fashion, especially in cold weather. In addition, pure castor oil is prone to undergo polymerization under casting conditions and deposit varnish-like films on molds and aluminum ingots leading to unsatisfactory surfaces and tears.
In order to perform satisfactorily on an industrial scale, a mold lubricant must meet several important requirements. Among these requirements are a viscosity at room temperature which allows easy and uniform application and a viscosity at mold-ingot interface temperatures sufficient to maintain a stable lubricant film. The lubricant must also have high resistance to thermal degradation. The lubricant must resist polymerization at high temperatures which lead to varnish-like deposits and unsatisfactory ingot surface. The lubricant must separate from ingot cooling water rapidly to avoid environmental contamination in discharge water and to avoid cooling problems in recirculated water. Aluminum ingot casting mold lubricants have generally not been able to satisfy all the foregoing requirements prior to the present invention.
Pure glycerol trioleate performs very satisfactorily as a continuous casting parting composition for aluminum and its alloys. However, at temperatures up to about 300.degree. C., the viscosity of glycerol trioleate is lower than that of castor oil. The low viscosity of glycerol trioleate has given rise to concern about possible leakage problems, particularly in warm weather.
Ingot casting lubricants are known in the prior art. Smith et al U.S. Pat. No. 3,524,751 claims an aluminum ingot casting lubricant comprising about 20 to 40% by weight of a lower alkyl ester of an acetylated hydroxy acid having 8 to 20 carbon atoms with about 80 to 60% by weight castor oil. A preferred embodiment involves a mixture of 25% n-butyl acetyl ricinoleate and 75% castor oil. This lubricant is marketed under the trade name Lubricin A-1.
Holshouser U.S. Pat. No. 3,034,186 claims an aluminum ingot casting lubricant which consists of boric acid dispersed in a suitable oily base material. In a preferred embodiment, 2 to 6% by weight of boric acid is mixed with lard oil.
It is a principal object of the present invention to provide a mold lubricant for casting aluminum and its alloys having an ambient temperature viscosity which obviates concern about leakage while permitting uniform application and a mold temperature viscosity sufficient to insure an uninterrupted lubricant film.
Related objects of the invention are to provide a lubricant accomplishing the foregoing objectives while at the same time having high thermal stability, good lubricity, rapid separation from ingot cooling water and avoidance of deposits on ingot and mold surfaces.
A further object of the invention is to provide a parting composition containing effective concentrations of additives such as oxidation inhibitors, biocides, copper corrosion inhibitors and the like, all of which are soluble in the composition itself.
Additional objects and advantages of the present invention will become apparent to persons skilled in the art from the following specification.